Chair back



FIG. 1 is a perspective view of a chair back showing my new design, itbeing understood that the broken line is for illustrative purposes onlyand forms no part of the claimed design; and,

FIG. 2 is an enlarged rear elevational view thereof with the lowerportion broken away for convenience of illustration.

FIG. 3 is a cross-sectional view taken along line 3-3 of FIG. 2 .

The ornamental design for a chair back, as shown and described.